The present invention is generally directed to colorant and toner processes, and more specifically, to processes which utilize aggregation and coalescence, or fusion of a latex, colorant, such as pigment, dye, or mixtures thereof, and optional additive particles. In embodiments, the present invention is directed to processes which provide toner compositions with a volume average diameter of from about 1 micron to about 25 microns, and preferably from about 2 microns to about 12 microns, and a narrow particle size distribution of, for example, about 1.10 to about 1.45 as measured by the Coulter Counter method. The resulting toners can be selected for known electrophotographic imaging and printing processes, including digital color processes.
The present invention in aspects thereof is directed to a process for the preparation of toners by mixing polymer encapsulated colorant particles and colorant particles, and more specifically, by blending an aqueous colorant, such as a pigment dispersion containing an ionic surfactant with a miniemulsion latex emulsion comprised of monomer particles, preferably submicron in size, of from, for example, about 100 nanometers to about 1,000 nanometers and preferably from about 200 nanometers to about 600 nanometers in volume average diameter, a nonionic surfactant and an ionic surfactant of opposite charge polarity to that of the ionic surfactant in the colorant dispersion, heating to accomplish polymerization of the monomer, thereafter heating the resulting mixture at, for example, below about the polymer glass transition temperature, and more specifically, from about 35.degree. C. to about 60.degree. C. (Centigrade) to form toner sized aggregates of from about 2 microns to about 20 microns in volume average diameter, and which toner is comprised of polymer, colorants, and optional additive particles, followed by heating the aggregate suspension above about the resin, or polymer glass transition temperature, and more specifically, at, for example, from about 70.degree. C. to about 100.degree. C. to effect coalescence or fusion of the components of the aggregates and to form mechanically stable integral toner particles. The miniemulsion contains, for example, a latex of water, polymer or resin, and colorant, oil, or monomer, water, surfactants, and preferably a cosurfactant, such as an alcohol, an alkane, an ether, an alcohol ester, an amine, a halide, or a carboxylic acid ester, which cosurfactant is preferably inert, nonvolatile, water insoluble, and is a liquid at a temperature of, for example, from about 40.degree. C. to about 90.degree. C., and contains a terminal aliphatic hydrocarbyl group with at least about 10 carbon atoms, and more specifically, from about 12 to about 24 carbon atoms, and mixtures thereof, and more specifically, an aliphatic alcohol with at least about 8 carbon atoms, such as from about 10 to about 25 carbon atoms, and an alkane with from about 10 to about 30 carbon atoms. The cosurfactant primarily functions to reduce the diffusion of monomer out of the monomer droplet and enables relatively stable miniemulsions since, it is believed, there is formed intermolecular complexes at the oil/water interface. The complexes are believed to be liquid condensed and electrically charged thus creating a low, for example from about 0.5 dyne/centimeter to about 5 dyne/centimeter interfacial tension and high resistance to droplet coalescence.
With the present invention in embodiments, there is selected a colorant encapsulated with polymer generated by miniemulsion polymerization process. Aggregation/coalescence of these colorant encapsulated polymer particles with colorant particles permit, for example, the generation of a wide range of colored toner compositions with, for example, high colorant loading, narrow particle size distribution, and excellent projection efficiency. Other advantages in embodiments include, for example, (1) better particle dispersion in the resin matrix; (2) improved mechanical properties; (3) protection of the colorant from outside influences during toner processing; and (4) protection of the matrix or toner resin from interaction with the colorant.
The aforementioned toners are especially useful for imaging processes, especially xerographic processes, which usually require high toner transfer efficiency, such as those having a compact machine design without a cleaner, or those that are designed to provide high quality colored images with excellent image resolution, improved signal-to-noise ratio, and image uniformity.